Exhaust manifold for internal combustion engines

ABSTRACT

An exhaust manifold which includes a flange to be fixed on an engine cylinder head. A wide exhaust gas collecting cavity is connected to the flange to receive exhaust gases discharged by exhaust pipes of the cylinder head. The wide collecting cavity has a recessed wall element subdividing the cavity into two mutually communicating sub-cavities. An end portion is connected to the collecting cavity outlet and has a discharge outlet for the exhaust gases.

BACKGROUND OF THE INVENTION

Field of the Invention

The invention relates to exhaust manifolds for internal combustionengines, and more particularly to those installed in internal combustionengines in association with a means for cleaning the exhaust gases, inparticular a start catalyst, which for example is mounted on themanifold.

SUMMARY OF THE INVENTION

One object of the invention is to provide such a manifold whose heatloss is as small as possible in order to shorten the time for startingthe cleaning means.

Another object of the invention is to ensure that the gas velocity fieldover the inlet face of the cleaning means is as uniform as possible.

Yet another object of the invention is to permit easy assembly of themanifold in the factory.

The invention therefore provides an exhaust manifold for internalcombustion engines. According to one general characteristic of theinvention, this manifold comprises a flange for fixation on the enginecylinder head, a wide exhaust-gas collecting cavity joined to the flangeto receive the exhaust gases delivered by the cylinder head exhaustpipes, this wide collecting cavity having a reentrant wall elementsubdividing the said cavity into two mutually communicatingsub-cavities. The manifold also comprises an end portion joined to thecollecting cavity outlet and having an outlet orifice for the exhaustgases.

The combination of the “plenum” form of the manifold (wide exhaust-gascollecting cavity) subdivided into two “lungs” ensures that the heatloss will be minimal and contributes to achieving a uniform velocityfield and uniform distribution of the exhaust gases at the inlet of agas cleaning means.

According to one embodiment of the invention, the reentrant wall elementprovides, on the outside surface of the collecting cavity, a centralindentation extending substantially perpendicular to the flange fixationplane, the two sub-cavities being symmetric with respect to the centralplane of this central indentation.

This embodiment thus not only makes it possible easily to construct thewide cavity formed by these two lungs but also permits, by virtue of thecentral indentation, easy introduction of a wrench for establishing apoint for fixation of the manifold on the cylinder head.

The wide collecting cavity has an appropriate internal volume. Moreparticularly, it has been found that it is advantageous for the volumeof the collecting cavity to be greater than about 0.8 times the cubiccapacity of the engine in order to achieve a noteworthy reduction ofheat loss as well as good uniformity of the velocity field at the inletof the cleaning means. In addition, and especially for reasons ofoverall size, it is preferable that the volume of the collecting cavitybe smaller than about 1.5 times the cubic capacity of the engine.

According to a preferred embodiment of the invention, the volume of thecollecting cavity is chosen substantially equal to the cubic capacity ofthe engine, thus permitting an optimal compromise between the criteriaof heat loss and uniformity of the velocity field and distribution, andoverall manifold size.

It is also particularly advantageous for the end portion to havesubstantially the form of a bowl, thus permitting the uniformity of thevelocity field to be further improved.

In addition, the end portion is preferably provided with an ellipticalthrottle plate, the major axis of the ellipse being parallel to theplane of fixation of the fixation flange. This also contributes toobtaining better uniformity of the velocity field.

The fixation flange is advantageously provided with four inlet ports toreceive the exhaust gases and with five points of fixation on thecylinder head, those points being disposed in crisscross arrangementaround the four inlet ports. Furthermore, the line segment connectingthe respective centers of two consecutive fixation zones passessubstantially through the center of the port situated between these twofixation zones.

Such an embodiment makes it possible to minimize the number of bolts forfixation of the manifold on the cylinder head and thus to minimize theassembly stresses associated with the introduction of wrenches. Inaddition, the criss-cross disposition of the fixation bolts relative tothe centers of two consecutive fixation zones aligned with the center ofthe inlet port situated between these two fixation zones contributes toensuring excellent leaktightness of fixation of the manifold on thecylinder head.

According to another embodiment of the invention, the manifold alsocomprises an intermediate connecting portion which connects the fixationflange to the collecting cavity and is provided with exhaust conduitsjoined respectively to the inlet ports of the fixation flange.Advantageously, the exhaust conduits disposed at the ends of theintermediate connecting portion are convergent. Consequently, all theexhaust conduits make it possible to force the exhaust-gas streamstoward the manifold center, thus additionally contributing toachievement of a uniform velocity field over the inlet face of thecleaning means. In addition, this intermediate connecting portioncontributes to increasing the rigidity of the manifold.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics of the invention will becomeevident upon examination of the detailed description of one embodiment,which in no way is limitative, and of the attached drawings, wherein:

FIG. 1 schematically shows a manifold according to the invention,

FIG. 2 is a section through line II—II of FIG. 1,

FIG. 3 is a section through line III—III of FIG. 2,

FIG. 4 shows the section of the throttle plate of the manifold throughline IV—IV of FIG. 2,

FIG. 5 shows a section through line V—V of FIG. 2,

FIG. 6 is a view in the direction of arrow F of FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In these FIGS., reference 1 denotes in general an exhaust manifoldaccording to the invention. This manifold is provided with a fixationflange 2 having five fixation holes 20 to 24, by means of which themanifold can be fixed by bolts onto the engine cylinder head.

The manifold is also provided with a wide exhaust-gas collecting cavity3, which is connected to the fixation flange by an intermediateconnecting portion 5.

This wide collecting cavity 3 is prolonged by an end connecting portion4 provided with a portion 41 having substantially the form of a bowlfollowed by a fixation flange 42 provided with an exhaust-gas outletorifice 49, a start catalyst CT being fixed, by welding in the presentcase, on the said fixation flange.

The outlet orifice 40 of bowl 41 is a throttle plate having ellipticalsection (FIG. 4), the major axis of the ellipse being parallel to theplane of fixation of the manifold on the cylinder head.

As illustrated more particularly in FIG. 3, the wide exhaust-gascollection cavity 3, which is cast in one piece, supports a reentrantwall element 32, which forms on the outside surface of cavity 3 acentral indentation 34, thus creating two symmetric lateral portions 30and 31. In this way collection cavity 3 is divided into two sub-cavities300 and 310, which are in mutual communication at the level ofconstricted section 320 of cavity 3, situated in the plane of symmetrythereof.

Central fixation zone 20 of fixation flange 2 is situated in theextension of central indentation 34, thus permitting introduction ofcentral wrench VS. In addition, lateral portions 30, 31 are providedwith reentrant wall elements 39, 38 respectively, which form on theoutside surface of these lateral portions two auxiliary indentations 37,36 respectively.

It will be noted here that fixation zones 22 and 23 are situatedrespectively in the extension of auxiliary indentations 37 and 36, thuspermitting easy introduction of automatic wrenches.

As illustrated more particularly in FIG. 5, it is evident that fixationflange 2 is provided with four ports O1 to O4 corresponding to the fourexhaust pipes made in the cylinder head and joined to the four cylindersof the engine. Fixation holes 20 to 24 are situated in criss-crosspattern around these ports O1 to O4. The center of each inlet port ofthe fixation flange is substantially aligned with the centers of the twofixation orifices disposed on both sides of this inlet port. Such anarrangement permits the number of manifold fixation bolts to beminimized while at the same time ensuring excellent leaktightness offixation on the cylinder head.

Intermediate connecting portion 5 is provided with four exhaust conduits51 to 54 prolonging the exhaust pipes of the cylinder head. Asillustrated more particularly in FIG. 6, axes A51 and A54 of the twoexhaust conduits situated at the end of intermediate connecting portion5 converge. Thus the entire group of exhaust conduits 51 to 54, and inparticular the two end conduits, ensure that the exhaust-gas streams areforced toward the manifold center.

Finally, at the top of collecting cavity 3, and in the extension of wallelement 32 and consequently of central indentation 34, there is disposeda port 35 for housing any desired transducer or sensor, especially asensor for measuring the oxygen concentration, commonly referred to as“lambda sensor” by those skilled in the art, which sensor is usedtraditionally in air/fuel ratio control circuits.

The location of this port 35 permits lambda sensor SL to be positionedcentrally, which is particularly advantageous.

The invention makes it possible to obtain an exhaust manifold withmounted-on start catalyst, which manifold is particularly efficient asregards heat loss and also as regards uniformity of the velocity fieldof the gases delivered to the start catalyst. In fact, except forexhaust conduits 51 to 54, which prolong the exhaust pipes for adistance of about 30 mm and incidentally contribute to ensuring goodmanifold rigidity because of this fact, the pulsations arriving from thefour cylinders are collected in a large volume and circulate towardoutlet orifice 40 of the bowl as illustrated by arrows CG in FIG. 3. Inaddition, bowl 41 permits even better homogenization of the gases,especially by causing vortexing action MC (FIG. 3) of the gases, thisbowl followed by elliptical throttle plate 40 contributing to thecreation of a uniform velocity field at the inlet of the start catalyst.

It will be understood that the invention as described hereinabove is notlimited to an exhaust manifold equipped with a mounted-on startcatalyst, but that it is also suitable for any gas cleaning means, suchas a three-way catalyst, a particulate filter, an NO_(x) trap, an SO_(x)trap, etc., whether it is mounted on the manifold or effectivelyconnected thereto by, for example, a tube portion.

What is claimed is:
 1. An exhaust manifold for internal combustionengines, characterized in that it comprises a flange for fixation on theengine cylinder head, a wide exhaust-gas collecting cavity joined to theflange to receive the exhaust gases delivered by the cylinder headexhaust pipes, this wide collecting cavity having a reentrant wallelement subdividing the said cavity into two mutually communicatingsub-cavities, as well as an end portion joined to the collecting cavityoutlet and having an outlet orifice for the exhaust gases, wherein eachsub-cavity is provided with an auxiliary reentrant wall element, whichforms on an outside surface of the corresponding sub-cavity an auxiliaryindentation, and wherein two of flange fixation zones are situatedrespectively in the extensions of the two auxiliary indentations.
 2. Amanifold according to claim 1, characterized in that the volume of thecollecting cavity is greater than about 0.8 times the cubic capacity ofthe engine and smaller than about 1.5 times the cubic capacity of theengine.
 3. A manifold according to claim 1, characterized in that theend portion is provided with a zone having substantially the form of abowl.
 4. A manifold according to claim 1, characterized in that the endportion is provided with a throttle plate of elliptical section, themajor axis of the ellipse being parallel to the plane of fixation of thefixation flange.
 5. A manifold according to claim 1, characterized inthat the fixation flange is provided with four inlet ports to receivethe exhaust gases and with five zones of fixation on the cylinder head,the said zones being disposed in criss-cross arrangement around the fourinlet ports, and in that the line segment connecting the respectivecenters of two consecutive fixation zones passes substantially throughthe center of the port situated between these two fixation zones.
 6. Amanifold according to claim 1, characterized in that the fixation flangeis provided with inlet ports to receive the exhaust gases, in that themanifold also comprises an intermediate connecting portion whichconnects the fixation flange to the collecting cavity and is providedwith exhaust conduits joined respectively to the inlet ports, and inthat the exhaust conduits disposed at the ends of the intermediateconnecting portion are convergent.
 7. A manifold according to claim 1,characterized in that the collecting cavity is provided with anadditional port for housing a sensor, disposed in the extension of thewall element.
 8. A manifold according to claim 1, characterized in thatthe reentrant wall element provides, on the outside surface of thecollecting cavity, a central indentation extending substantiallyperpendicular to the flange fixation plane, and in that the twosub-cavities, are symmetric with respect to the central plane of thiscentral indentation.
 9. A manifold according to claim 8, characterizedin that a central fixation zone of the fixation flange is situated inthe extension of the central indentation.